As part of the nutritional survey of the Canary Islands (ENCA-1998), the concentrations in serum of Na, K, Ca and P were determined in 395 individuals representing the population of the Canary Islands. The concentrations were found to be within the reference intervals described for the healthy population. Differences were observed in the mean concentrations depending on the island of residence. Thus, individuals on the island of Tenerife showed higher levels of natremia and calcaemia (p < 0.05) than those on the other islands. The islanders of La Palma have the highest (p < 0.05) and lowest (p < 0.05) concentrations of K and Ca, respectively, whereas those living on the easternmost islands have the highest levels of phosphataemia. No differences were detected in the mineral levels by sex. Phosphataemia levels fall (p < 0.05) in line with socio-economic levels. Females under the age of 18 present lower levels of natremia (p < 0.05) than others while males over the age of 35 present higher levels of kalaemia (p < 0.05). No important age-related differences were found in calcaemia and individuals under the age of 18 had lower levels of phosphataemia (p < 0.05) than the remainder. Highly significant relationships were found between Na and K and between Ca and P, thus confirming existing physiological relationships. Smoking had no effect on the serum levels of the elements under study. Those individuals reporting an intake of more than seven beers and seven shots of spirit per week presented lower levels of calcaemia and natremia than the rest (p < 0.05). With wine consumption, an increase in kalaemia and a significant reduction (p < 0.05) in the Na/K ratio were detected. Individuals drinking only tap water had higher levels (p < 0.05) of natraemia and kalaemia, with lower levels (p < 0.05) of calcaemia and the Na/K ratio than those drinking bottled water. The Ca/P ratio was significantly reduced (p < 0.05) with physical exercise.